Voyager 2 beams back intriguing data on Uranus

By , Staff writer of The Christian Science Monitor

Voyager 2, the hardy, long-lasting planetary explorer, is fit and ready to take a close look at Uranus next month. Officials of the National Aeronautics and Space Administration (NASA) report that not only is the 1,819-pound robot spacecraft working well mechanically and electronically, it already is returning intriguing data on the distant planet.

Voyager 2 will zip past Uranus and its five moons, coming within 50,600 miles of the planet, on Jan. 24. However, for Voyager scientists, the encounter with Uranus started Nov. 4, when the spacecraft began scanning the planet, and continues through next Feb. 25, when Voyager finally abandons its scrutiny as it heads for Neptune.

The spacecraft has already glimpsed Uranus's rings. Voyager continues to mystify scientists, as it has for more than a month, by its failure to detect any radio noise coming from the planet

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The International Ultraviolet Explorer satellite, launched in 1978, has detected what appear to be aurorae at Uranus. Aurorae are caused by charged particles trapped in a planet's magnetic field. So scientists assume Uranus has a substantial magnetosphere -- a zone dominated by its magnetic forces. A magnetosphere should also emit strong radio noise. But Michael Kaiser and Michael Desch of the NASA Goddard Space Flight Center in Greenbelt, Md., have reported that Voyager 2 sensors are finding only radio

silence.

Either scientists are wrong to assume Uranus has strong magnetism or the planet's magnetosphere is shaped so as to emit its radio noise only on its night side, which now faces away from Earth and the spacecraft.

Puzzles such as this only stimulate scientists' anticipation of Voyager's close-in inspection. Twenty times farther from the Sun than Earth, Uranus is so distant that astronomers have never seen it as more than a fuzzy disk. Thus much of what Voyager finds out about the solar system's third largest planet is apt to be a revelation.

Uranus, some 32,000 miles in diameter and surrounded by nine known rings, lies on its side in its orbit. When Earth-based observers look at the planet, they are seeing its south pole, more or less. Voyager 2 will flash through the Uranian system at more than 45,000 miles an hour like an arrow flying through a hoop. Its equipment must function smoothly to make the most of the few hours during which it will be close to its targets.

Voyager lost one of its two radio receivers within a year of its launch in 1977. A gear in its moveable instrument platform became stuck for a while during its Saturn flyby in 1981. Project manager Richard P. Laeser of NASA's Jet Propulsion Laboratory in Pasadena, Calif., says Voyager engineers understand these problems well and have firm control of the spacecraft. Furthermore, he explains, ``We have developed a technique to detect the onset of a problem and alternative techniques for pointing the space craft if we get a last-minute failure.''

NASA officials such as Richard Laeser often cite Voyager as one of their most cost-effective spacecraft. Originally designed only to explore Jupiter and Saturn, a mission that cost $360 million, rugged construction and skillful handling by flight engineers have enabled it to go on to Uranus. Ultimately, flight engineers hope it will continue to operate as it heads toward Neptune.

The added cost of exploring Uranus is only $86 million. Uranus's gravity will deflect the craft on to Neptune for an encounter Aug. 24, 1989. That exploration will cost another $100 million. So Voyager is picking up two more planets for about half the cost of its original mission.

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